Preliminary studies indicate that women with fibroadenoma of the breast are at increased risk of developing breast cancer, and that women with fibroadenoma in combination with other risk factors may be at elevent times the normal breast cancer risk. We propose to perform a retrospective cohort study of voer 1000 women who presented with fibroadenomas at one of three Nashville hospitals between 1950 and 1968. All patients who had a biopsy confirmed fibroadenoma that was not preceded by or diagnosed concurrently with invasive breast cancer will be included in this study if: the slides from her biopsy contained evaluable breast parenchyma; she did not undergo amputation of both breasts or develop invasive breast cancer within 6 months of ther initial biopsy; and her surgeon did not discard old or inactive records from the recruitment years of the study. We estimate that at least 1000 women will meet these criteria. In addition, we will also follow-up an equal number of control patients who will be matched for age and year of presentation with our fibroadenoma subjects. Each control patient will be drawn from the sdame surgical practice as her matched fibroadenoma counterpart. She must have presented to her surgeon with a complaint that did not concern her breasts and which did not result in a diagnosis of cancer. Also, she must not have undergone breast surgery prior to the histologic changes found within the fibroadenoma as well as in the adjacent parenchyma. This review will also include all biopsies for fibroadenoma patients who were not selected for our follow-up. Information on subsequent breast cancer outcome and on non-anatomic risk factors will then be obtained through patient follow-up. Our previous experience indicates that we can obtain a follow-up rate of 95%. After follow-up is completed, our data base will be analyzed using hazard regression methods and other statistical techniques that can elucidate the cancer risks associated with various constellations of risk factors from a longitudinal data base. We believe that we can identify groups of women at high risk of developing breast cancer (Relative Risk in range of 10 times the general population) who can be identified through a diagnosis of fibroadenoma and other risk factors.